That is the picture delivered by data from the government'sstatistics office. But it is not a picture which would berecognised by many Saudi companies, which saw their profitscrimped by a crackdown on illegal workers late last year, and itis not in line with private surveys of business activity.

So many economists have concluded that the official data isfaulty in some way, and that actual Saudi GDP in the fourthquarter may be billions of dollars lower than the statisticsoffice suggests. But it is not clear when, or whether, themystery will be solved.

As the wealthy Gulf Arab oil exporters boom and open widerto foreign investment, investors are operating in something of afog: they must base their judgements on patchy and erraticmacroeconomic data. In many cases the data is less reliable thannumbers provided by emerging economies in Asia and Africa.

In the Gulf, preliminary figures for economic indicators canbe off the mark but revisions may occur only many months later,if at all. Release times are irregular; Bahrain has notannounced its monthly money supply data since November.

Some data series have been suspended for a few months beforeresuming. Other data just does not exist. Kuwait, for example,does not regularly publish GDP growth figures, making it almostunique among the world's rich countries.

Because of the region's oil wealth, economies have so fargrown without many visible ill effects. But the costs of havingsuch poor data may increase as the Gulf states develop theirfinancial markets and diversify their economies in an effort tobecome less vulnerable to the next big drop in oil prices.

"The regional central banks have to understand thattimeliness and consistency, and scientific production of data,are a necessity if they want to show they are open forinvestment and business," said John Sfakianakis, chiefinvestment strategist at MASIC, a Riyadh-based investment firm.

A lack of reliable figures for government spending can hurtinvestment because many firms base their decisions on the levelof that spending, he added. Abu Dhabi, which accounts for some70 percent of state spending in the United Arab Emirates, doesnot publish its annual budget plans in a comprehensive manner.

REASONS

The Gulf countries have enough money to create agenciescompiling accurate, regular statistics if they wish. So thereasons for the data problem appear complex.

The biggest reason may be simply that governments see nostrong need for data. Economies are still driven by oilrevenues, which depend mainly on external rather than domesticdemand. Monetary policy is basic, with central banks rarelyadjusting interest rates or liquidity supplies.

Since authorities are not continually fine-tuning policiesin response to economic trends, they do not view collectingtimely, detailed data as a priority.

Also, because of their reliance on oil revenues, Gulfgovernments generally do not collect individual income orvalue-added taxes. Tax systems are a key source of raw numbersfor economic statistics in other countries.

Many Gulf companies have secretive cultures and arereluctant to disclose any information on their business, even togovernments - a major headache for state statisticians.

An additional factor may be the secretive nature of the Gulfgovernments themselves, which tend not to debate sensitiveissues in public. In some cases, they may be accumulating databut choosing not to reveal it, or not bothering to do so.

"A lot of data is collected, so it is available for policymakers, but is not published," said Paul Gamble, director in thesovereign group at credit rating agency Fitch Ratings.

Authorities are making efforts to strengthen their dataservices; the emirate of Abu Dhabi, for example, has launched acomprehensive public statistics website over the last few years.Gamble said Gulf data had improved enough over the past decade"to give a broad guide to economic performance".

But policy makers and businessmen still face puzzles such asSaudi Arabia's fourth-quarter GDP. The government's statisticsoffice announced that the country's GDP grew 3.8 percent in2013, but did not give a number for the fourth quarter.Calculations by Reuters and private economists show the 2013figure can only be reconciled with the data for the first threequarters if fourth-quarter growth is a sky-high 10 percent.